An Ab-initio study of the Y decorated 2D holey graphyne for hydrogen storage application

Abstract: Expanding pollution and rapid consumption of natural reservoirs (gas, oil, and coal) led humankind to explore alternative energy fuels like hydrogen fuel. Solid-state hydrogen storage is most desirable because of its usefulness in the onboard vehicle. In this work, we explored the yttrium decorated ultra porous, two-dimensional holey-graphyne for hydrogen storage. Using the first principles DFT simulations, we predict that yttrium doped holey graphyne can adsorb up to seven hydrogen molecules per yttrium atom resulting in a gravimetric hydrogen weight percentage of 9.34, higher than the target of 6.5 wt% set by the US Department of Energy (DoE). The average binding energy per H$_2$ and desorption temperature come out to be -0.34 eV and ~ 438 K, respectively. Yttrium atom is bonded strongly on HGY sheet due to charge transfer from Y 4d orbital to C 2p orbital whereas the adsorption of H$_2$ molecule on Y is due to Kubas-type interactions involving charge donation from H 1s orbital to Y 3d orbital and back donation with net charge gain by H 1s orbital. Furthermore, sufficient energy barriers for metal atom diffusion have been found to prevent the clustering of transition metal (yttrium) on the HGY sheet. The stability of the system at higher temperatures is analyzed using Ab-initio molecular dynamics (AIMD) method and the system is found to be stable at room and the highest desorption temperature. Stability of the system at higher temperatures, presence of adequate diffusion energy barrier to prevent metal-metal clustering, high gravimetric wt% of H$_2$ uptake with suitable binding energy, and desorption temperature signifies that Y-doped HGY is a promising material to fabricate high capacity hydrogen storage devices.